This invention relates to metal halide arc discharge lamps generally and more particularly to a novel construction for such type lamp to provide improved illumination when operated from a generally horizontal position.
Metal halide arc discharge lamps are now employed globally as a source of highly efficient white and colored light in a wide variety of lighting applications. These versatile lamps can be used outdoors as well as indoors equally well with typical temperature extremes having little or no impact on illumination performance. Because these lamps also produce substantially less heat than incandescent lamps for a given light level, the heat reduction therefrom reduces the amount of energy required to cool an indoor lighted place. Their versatility, compact size and long life has further been recognized for replacement of high pressure sodium vapor lamps in existing fixtures without need to change ballasts, igniters or even replace the existing sockets in order to gain a source of more natural color illumination. Accordingly, these lamps have already been found useful over the widest possible range of lighting applications to include outdoor lighting of buildings, billboards, roadways and sport fields as well as indoor lighting of commercial offices, warehouses and manufacturing facilities.
When intended for operation in a horizontal position this type lamp can be constructed with position oriented base means such as a locating pin being affixed to a screw-in base member to provide a spatial engagement in the lamp fixture assisting the lamp performance. When operated in a horizontal orientation, still other factors not generally experienced with vertical lamp operation have been found to deter optimum lamp performance. To still further illustrate such distinct operational factors, there is disclosed in U.S. Pat. No. 5,055,740 a horizontal burning metal halide lamp construction which largely avoids most of the significant problems encountered with horizontal lamp orientation. More particularly, the disclosed lamp construction features a generally cylindrical arc tube member having electrodes at the ends positioned below the longitudinal central axis of the arc tube in combination with an asymmetric contour of the arc tube ends. A heat reflective coating of said arc tube ends is further disclosed in such prior art lamp construction to improve the lamp performance.
A still further serious operational problem has been found to exist with metal halide arc discharge lamps constructed in the foregoing manner upon being operated in a generally horizontal position. By "generally horizontal position" as used in the present application is meant a spatial orientation of the lamp device so that the longitudinal central axis of its arc tube during operation can be tilted above and below the horizontal axis by as much as sixty degrees. Specifically, it has now been found that horizontal operation of the conventional lamps is accompanied by a rapid fluctuation or wavering of the bowed arc discharge within the arc tube causing undesirable movement of light output from the lamp. The disconcerting nature in such rapid light movement is visibly observable hence could prove highly objectionable to both spectators and athletes at sporting events as well as to occupants of an industrial or commercial work place.
Accordingly, one object of the present invention is to obviate light output fluctuation in horizontal burning metal halide arc discharge lamps with a novel lamp construction.
It is another object of the present invention to provide an improved arc tube construction for a metal halide arc discharge lamp which is not subject to light output fluctuations during horizontal burning.
A still further object of the present invention is to provide a novel horizontal burning metal halide arc discharge lamp construction eliminating light output fluctuations by means of modifying the arc tube configuration during fabrication.
Still another object of the present invention is to provide a relatively simple modification in otherwise conventional lamp manufacture enabling improved construction of a horizontal burning metal halide arc discharge lamp.
These and still further objects of the present invention will become apparent upon considering the following detailed description for the present invention.